1066. Root of AVL Tree (25)

时间限制 100 ms

内存限制 65536 kB

代码长度限制 16000 B

判题程序
Standard 作者 CHEN, Yue

An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Figures 1-4 illustrate the rotation rules.

Now given a sequence of insertions, you are supposed to tell the root of the resulting AVL tree.

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=20) which is the total number of keys to be inserted. Then N distinct integer keys are given in the next line. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print ythe root of the resulting AVL tree in one line.

Sample Input 1:

5
88 70 61 96 120

Sample Output 1:

70

Sample Input 2:

7
88 70 61 96 120 90 65

Sample Output 2:

88

提交代码

知识点：（1）AVL（平衡二叉树）。 （2） AVL树的建立，请参考这篇博文： http://blog.csdn.net/gabriel1026/article/details/6311339       。

请结合图文参考一下代码：

#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <cstring>
#define PI acos(-1)
#define inf 0x3f3f3f3f
#define SCD(a) scanf("%d",&a)
#define SCDD(a,b) scanf("%d%d",&a,&b)
#define SCF(a) scanf("%lf",&a)
#define PTD(a) printf("%d\n",a)
#define PTS(a) printf("%s\n",a)
#define MST(a,b) memset(a, b, sizeof(a))
using namespace std;
//                      PTA (Advanced Level) Practise 1066 Root of AVL Tree (25)

const int L = 10010;

struct AVLNode{
    int data;
    AVLNode* lchild;
    AVLNode* rchild;
};
AVLNode* T;

void LL(AVLNode* &T)
{
    AVLNode* t = T->rchild;
    T->rchild = t->lchild;
    t->lchild = T;
    T = t;
}

void RR(AVLNode* &T)
{
    AVLNode* t = T->lchild;
    T->lchild = t->rchild;
    t->rchild = T;
    T = t;
}

void RL(AVLNode* &T)
{
    RR(T->rchild);
    LL(T);
}

void LR(AVLNode* &T)
{
    LL(T->lchild);
    RR(T);
}

int Height(AVLNode* &T)
{
    if(!T)
        return 0;
    return max( Height(T->lchild), Height(T->rchild) ) + 1;
}

void InsertAVLNode(AVLNode* &T, int val)
{
    if(!T){
        T = new AVLNode;
        T->data = val;
        T->lchild = NULL;
        T->rchild = NULL;
        return;
    }
    if(val < T->data){
        InsertAVLNode(T->lchild, val);
        if(Height(T->lchild) - Height(T->rchild) == 2){
            if(val < T->lchild->data)
                RR(T);
            else
                LR(T);
        }
    }else{
        InsertAVLNode(T->rchild, val);
        if(Height(T->rchild) - Height(T->lchild) == 2){
            if(val > T->rchild->data)
                LL(T);
            else
                RL(T);
        }
    }
}

int main()
{
    int i, b, t, j, n;
    SCD(n);
    for(i=0;i<n;i++){
        SCD(t);
        InsertAVLNode(T, t);
    }
    PTD(T->data);
}